DESCRIPTION (from page 2 of the application): The general goal of this research is to advance understanding of cochlear mechanics, especially the functioning of the 'cochlear amplifier'. This is the name given to the set of active, vulnerable processes which provide the mammalian cochlea with its exquisite sensitivity, frequency resolution and range compression. Dysfunction's of the cochlear amplifier are the leading cause of human deafness, and better understanding of its basic processes are expected to lead to improved methods of prevention and treatment of hearing dysfunction. The specific aim of the proposed research is to use the development of cochlear function in neonatal gerbils as a method of investigation of cochlear mechanics., Answers are sought to the following related set of questions. How do the functional characteristics of the cochlear amplifier change during development, especially in relationship to developmental changes in the endocochlear potential (EP) and in the frequency-place map? How do the same characteristics change with related external manipulations, such as furosimide-induced changes in EP? What is the nature of the processes which act to establish or to control the characteristics of the cochlear amplifier? Can it be established that the same processes are at work during development as those seen after external EP change, where there is observed to be a functional adaptation to a low EP? Is there any evidence that such putative adaptation mechanisms depend on the afferent-efferent feedback system? Is there evidence for the hypothesis that these control functions are functional feedback mechanisms, i.e., mechanisms which might act to set the cochlear amplifier gain to optimum values as a function of frequency? The primary tool for these experiments involves the use of two and three tone distortion product otoacoustic emissions to measure cochlear characteristics. Specific experiments include determination of 1) significant changes during development of cochlear amplifier characteristics, especially gain and tuning width; 2) the relationship of active to passive cochlear characteristics during development, particularly during periods of rapid frequency-place changes; 3) changes in cochlear amplifier characteristics caused by a manipulation of the EP, with particular attention to the proposed adaptation process; 4) the effect on the normal cochlear function, and on functional recovery to EP change, of a block on activity of the cochlear nerve.